ServiceDesk sd.use.search.by.permissions feature flag might cause slow user picker search

Summary

Closed Access Service Desks with sd.use.search.by.permissions feature flag set (default), might have slow user picker search.
see KB for more details: Closed Access Service Desks, slow user picker search

Environment

• a large number of users 10k+
• The dark feature sd.use.search.by.permissions.disabled is not activated.
• Closed Access ServiceDesks
  • Who can raise requests? set to Customers who are added to the project.

Expected Results

User picker search is fast and doesn't have extra memory/SQL pressure

Actual Results

User picker search can be slow and have extra memory (see JSDSERVER-5958)/SQL pressure

Notes

• In case of Closed Servicedesk, code takes users by permission and does additional filtering. Unfortunately, increased memory consumption (and interoperability with lazy user cache) wasn't taken into account.
• Overall disabling of this feature flag doesn't affect search results but has an effect on performance. With it disabled open and closed servicedesk will go through the same execution path.

Workaround

• Disable "sd.use.search.by.permissions" feature flag, see KB Closed Access Service Desks, slow user picker search